# The String Theory Landscape

## Abstract

**:**

## 1. Introduction

**three**factors. The first is a sum over vacua, while the second “cosmological” factor, call this $U\left(i\right)$, is the expected number of universes in the multiverse which realize the vacuum ${V}_{i}$. The third “anthropic” factor, which we call $A\left(i\right)$, is the expected number of observers in a universe of type i. We can then write the expectation value of an observable O as

## 2. String Compactification and the Effective Potential

_{3}constructions.

_{3}; it is

#### Problems with the String Compactification Analysis

## 3. Eternal Inflation and Measure Factor

#### Problems with the Eternal Inflation Analysis

## Funding

## Acknowledgments

## Conflicts of Interest

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1. | We might impose additional physical conditions if convenient, such as positive cosmological constant. |

2. | Some observables, for example $\delta \rho /\rho $, do depend on the early history of the universe. To discuss these we would need to generalize Equation (1), but we can still work in terms of the four dimensional degrees of freedom visible in the vacuum ${V}_{i}$. |

3. | Kachru, Kallosh, Linde and Trivedi. |

4. | There are several arguments that complex vacua might be disfavored; see [63]. |

5. | See also the article [8] in this issue. |

6. | Our point was not to claim that the multiverse is a simulation, in fact we explicitly postulate that no local observer can tell that the multiverse is being simulated. Rather, in the spirit of computational complexity theory, the point is to define the complexity of the multiverse in terms of a “reduction” to another problem whose complexity we know how to define, namely that of running a specified quantum computer program. |

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**MDPI and ACS Style**

Douglas, M.R.
The String Theory Landscape. *Universe* **2019**, *5*, 176.
https://doi.org/10.3390/universe5070176

**AMA Style**

Douglas MR.
The String Theory Landscape. *Universe*. 2019; 5(7):176.
https://doi.org/10.3390/universe5070176

**Chicago/Turabian Style**

Douglas, Michael R.
2019. "The String Theory Landscape" *Universe* 5, no. 7: 176.
https://doi.org/10.3390/universe5070176